Sheet Material, Mold, and Methods of Making and Using the Sheet Material and Mold

ABSTRACT

A one-piece component comprising a tetrahedral-octahedral honeycomb lattice is disclosed herein, along with a mold, a system and methods of making the component. A one-piece component comprising a truncated tetrahedral-octahedral honeycomb lattice also is disclosed, along with corresponding molds, systems and methods.

BACKGROUND

While many core producers have been aware of the isotropic strengthproperties inherent in a Tetrahedral-Octahedral Honeycomb Lattice-basedcore material, most of the manufacturing processes proposed/employed todate involve molding a top and bottom sheet of material with tetrahedralelements and bonding them together to create a multi-piece core/lattice.U.S. Pat. Nos. 3,642,566 and 3,689,345 disclose known processes thatinvolve connecting two sheets to form a core material. This approachruns the risk of core failure due to delamination and is difficult andexpensive to manufacture. Alternatively, filament winding has beenproposed, as is described in U.S. Pat. Nos. 3,657,059 and 3,645,833, butthis too is time consuming and expensive. Further efforts to produceisotropic core material are described in U.S. Pat. No. 4,020,205, whichdescribes manufacturing the core material by bending continuous stripsof ribbon having lateral offset sections to form triangular sides andoccluded dihedral angles of alternating tetrahedrons and octahedrons.

The interest in and use of lightweight composite materials has steadilygrown over the last 40 years driven by the need to reduce weight in arange of structural products used by the marine, aerospace andtransportation industries, among others. Common core materials used incomposites include foam, aluminum honeycomb, Nomex honeycomb, balsawood, and plywood among others. While each of these core materials hassatisfied the needs of various applications, there remains a need for alightweight, isotropic or quasi-isotropic, inherently rigid, corematerial that can be molded at low cost and in high volume.

SUMMARY

One embodiment described herein is a one-piece component comprising atetrahedral-octahedral honeycomb lattice.

Another embodiment is a one-piece component comprising a truncatedtetrahedral-octahedral honeycomb lattice. Yet another embodiment is astructure that includes a one-piece component comprising atetrahedral-octahedral honeycomb lattice and/or a truncatedtetrahedral-octahedral honeycomb lattice.

A further embodiment is a mold configured to form a one-piece componentcomprising a tetrahedral-octahedral honeycomb lattice and/or a truncatedtetrahedral-octahedral honeycomb lattice. In embodiments, the moldincludes a first portion with a base having a first set of tetrahedraland inclined pyramidal protrusions formed thereon, and a second portionwith a base having a second set of tetrahedral and inclined pyramidalprotrusions formed thereon, wherein the first and second sets oftetrahedral and pyramidal protrusions are complementary, and wherein theinclined pyramidal protrusions comprise a rectangular first surfaceportion and triangular second, third and fourth surface portions. Inembodiments, during use, the rectangular first surface portion of eachinclined pyramidal protrusion formed on the first portion of the mold isadjacent to and in contact with a rectangular first surface portion ofan inclined pyramidal protrusion formed on the second portion of themold. In embodiments, the first and second portions of the mold areconfigured to separate in opposite diagonal directions that are parallelto the plane of the rectangular first surface portions of the inclinedpyramidal protrusions.

Yet another embodiment is an apparatus comprising a first portion with abase having a first set of tetrahedral and inclined pyramidalprotrusions formed thereon, and a second portion with a base having asecond set of tetrahedral and pyramidal protrusions formed thereon,wherein the first and second sets of tetrahedral and pyramidalprotrusions are complementary and positioned adjacent to one another,forming a lattice-shaped void therebetween, and wherein the inclinedpyramidal protrusions comprise a rectangular first surface portion andtriangular second, third and fourth surface portions.

A further embodiment is a method of making a component, comprisingobtaining a mold comprising the apparatus described in the previousparagraph, filling the mold with a liquid or molten moldable material,allowing the moldable material to solidify to form the component, andremoving the component from the mold. In embodiments, the moldablematerial comprises at least one of a thermoplastic polymer and athermoset polymer. In embodiments, the component is post-treated.

Another embodiment is a method of forming a component comprising atetrahedral-octahedral honeycomb lattice or a truncatedtetrahedral-octahedral honeycomb lattice using additive manufacturing.In embodiments, the component is post-treated. A further embodiment is atetrahedral-octahedral honeycomb lattice or a truncatedtetrahedral-octahedral honeycomb lattice formed by additivemanufacturing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a sheet according to a firstembodiment.

FIGS. 2A-2D show symmetric side views of the sheet of FIG. 1.

FIGS. 2E-2G show asymmetric side views of the sheet of FIG. 1.

FIG. 3 is a top plan view of the sheet of FIG. 1.

FIG. 4 shows a perspective view of a sheet in accordance with a secondembodiment, having a truncated tetrahedral configuration.

FIG. 5A-5B show symmetric side views of the sheet of FIG. 4.

FIGS. 5C-5D show asymmetric side views of the sheet of FIG. 4.

FIG. 5E is a side perspective view of the sheet of FIG. 4.

FIG. 6 is a top plan view of the sheet of FIG. 4.

FIG. 7A is a perspective view of a prototype of a first embodiment oftwo halves of a mold for forming a sheet, the halves being positionednext to one another in a perpendicular arrangement.

FIG. 7B shows the mold of FIG. 7A in a closed position.

FIG. 7C shows the mold of FIG. 7A in a closed position with slatsshowing the spaces where sheet material fills the mold.

FIG. 7D shows the mold of FIG. 7A in a partially open position.

FIG. 7E shows the mold of FIG. 7A in an open position.

FIG. 7F is a top view of a mold half showing the relative alignment ofthe tetrahedral and pyramidal portions.

FIG. 8 is a schematic side sectional view of two mold halves similar tothat shown in FIG. 7 with a molded sheet therebetween.

FIG. 9 is a schematic side sectional view showing diagonally upwardmovement of the first mold section in order to remove the sheet.

FIG. 10 is a schematic side sectional view showing the angled directionof ejection of the sheet from the second mold half.

FIG. 11 is a schematic side section view showing movement of the lowermold section away from the molded sheet.

FIG. 12A is a schematic side sectional view showing simultaneousmovement of the two mold halves away from the sheet.

FIG. 12B is a schematic side view of a mold with vertical pulls forforming the sheet of FIG. 1.

FIG. 13 is a schematic side view of two mold halves of a vertical pullmold for forming a sheet of truncated configuration with a sheet moldedtherebetween.

FIG. 14 is a schematic side view showing upward movement of the secondmold half in order to remove the sheet.

FIG. 15 is a schematic side view showing the vertical direction ofejection of the sheet from the second mold half.

FIG. 16 is a schematic side view showing movement of the first moldsection away from the sheet.

FIG. 17 is a schematic side sectional view showing simultaneous movementof the two mold halves away from the sheet.

FIG. 18 is a top view of an embodiment of sheet material having closedsides.

FIG. 19 is a table showing simulation data for non-truncated andtruncated sandwich core material.

FIG. 20 is a table showing simulation data, including beam load andshear load data for non-truncated and truncated sandwich core material.

DETAILED DESCRIPTION

The embodiments described herein demonstrate a mold design that makes itpossible to directly mold a tetrahedral-octahedral honeycomb lattice foruse in commercial applications. Methods of making the product and theresulting product also are described.

In some cases, the product is a one-piece core or sheet comprising alattice of material (including but not limited to a thermoplastic resin,thermoset material, thermoplastic elastomer, carbon fiber, metals,including but not limited to aluminum, steel, cardboard, rubber,concrete or any other material suitable for applications requiring anengineered structure) where the lattice is comprised of intersectingrows of parallel slats of material oriented along 3 distinct andintersecting sets of parallel planes, such that any 3 of the slat planeswhich are not parallel intersect to form an equilateral, regulartetrahedron. Non-limiting examples of suitable thermoplastic materialsinclude polymers such as polyethylenes, polypropylenes, polyvinylchlorides, nylons, ABS, polylactic acid, acrylics, polycarbonates,polystyrenes, polyethers, polyphenylenes, as well as copolymers andterpolymers of the same. Non-limiting examples of suitable thermosetmaterials include polymers such as natural and synthetic rubber, vinylesters, polyesters, thermosetting acrylic resins, polyurethanes andepoxies. Non-limiting examples of suitable thermoplastic elastomersinclude olefinic thermoplastic elastomers, styrene block copolymers,thermoplastic copolyesters, and thermoplastic polyamides. Fillers andother additives can be included with the polymeric materials. Thepolymeric material can be a foam, and can molded using structural foammolding or another suitable technique.

The adjacent parallel slats are separated by a constant distance, xo,where xo is the same for all of the adjacent parallel slats orientedacross all 3 distinct sets of parallel planes. For a top view, see FIG.3 below.

Definitions

Platonic Solid: A polyhedron constructed of congruent, regular polygonalfaces. The same number of faces must meet at each vertex of the faces ofthe polyhedron. The regular congruent tetrahedron and the regularcongruent octahedron are both Platonic solids.

Regular Convex Tetrahedron (RCT): A platonic solid having 4 regulartriangular faces.

Irregular Tetrahedron: A tetrahedron with 4 triangular faces, at leastone of which is not an equilateral triangle. An irregular tetrahedronhas six edges and four vertices.

Regular Convex Octahedron (RCO): A platonic solid having 8 regulartriangular faces.

Irregular Octahedron: An octahedron with 8 triangular faces, at leastone of which is not an equilateral triangle. An irregular octahedron hastwelve edges and six vertices.

Pyramid: One half of an RCO comprised of a square base and 4 of the 8regular triangular faces of the RCO defining the sides. Two pyramidswith adjoining square bases form an RCO.

Tessellation: A pattern of shapes that fit perfectly together(mathisfun.com). A tessellation of tetrahedrons and octahedrons can beformed by alternating the octahedrons with tetrahedrons in successiveoffsetting rows where half of the tetrahedrons have their verticespointed downward and half have their vertices pointing upward. The facesof the tetrahedrons and octahedrons form multiple parallel linear facesacross the tessellation oriented in only 3 of the non-horizontaldirections corresponding to the three non-base faces of any/all of thetetrahedrons. These parallel linear faces define slats that make up thelattice that is molded to become the final Tetrahedral-OctahedralHoneycomb lattice core material.

Tetrahedral-Octahedral Honeycomb: A tessellation of RCT and RCO wherethe faces are congruent. The focus of this document is a 3-dimensional,single layered tessellation of RCT and RCO.

Tetrahedral—Octahedral Honeycomb Lattice: The space falling between theRCO and RCT in a Tetrahedral-Octahedral tessellation. This is the spaceinto which material is injected to mold the Tetrahedral-OctahedralHoneycomb lattice. Alternatively, it is the space left void to form alattice when the objective is to create a lattice of space for uniformlydisbursing liquids, gases or other flowing materials.

Dihedral Angle: The angle between two intersecting planes. The dihedralangle of a regular convex tetrahedron or a regular convex octahedron isthe interior angle between two adjacent face planes. The dihedral angleof a regular convex tetrahedron is 70.53 degrees. The dihedral angle ofa regular convex octahedron is 109.47 degrees. The dihedral angle of aright regular pyramid between the square base and a triangular side is54.735 degrees.

Isotropic: Exhibiting properties with the same values when measuredalong axes in all directions (Merriam Webster); in physics, an object orsubstance having a physical property that has the same value whenmeasured in different directions (Oxford Dictionaries).

One-piece: Formed as a unitary component in a molding process, withoutrequiring lamination or adhesion of two or more sub-parts.

Sheet: A three-dimensional lattice with planar or curved top and bottomfaces.

The product comprises a one-piece Tetrahedral-Octahedral HoneycombLattice Core, because the negative space between the intersecting slatscomprising the lattice are alternating rows of tetrahedra and octahedra.The rows of tetrahedra alternate between being pointed upwards andpointed downwards. These alternating rows of tetrahedra and octahedraform a tetrahedral-octahedral tessellation as the width of the latticeslats converges on 0. Conversely, as the space between the platonicsolids forming the tetrahedral-octahedral tessellation is expanded,material can be injected or otherwise inserted into the space to form aTetrahedral-Octahedral Honeycomb Lattice. The Lattice that is formedmakes a highly desirable, quasi-isotropic, rigid core material.Importantly, the core geometry is inherently rigid, independent of beingsandwiched between surface and base layers in a laminate structure. Soas a result, it can enhance the rigidity of a composite laminate whenused as a core, versus other core materials structured aroundalternative geometries.

The strength of the core, for any given material, is a function of thespacing between the slats and the width of the slats themselves, inaddition to the material from which the core is made. The height of thecore is primarily a function of the distance between the slats (xo).That said, by shaving or truncating the top and bottom of the latticestructure, the lattice height can be reduced and weight removed. Byincreasing the width of the slats, the loss of strength due totruncation can be compensated for, albeit while adding additionalweight. If truncated, the negative space of the lattice formsalternating truncated tetrahedra and octahedra. By varying the corematerial, the width of the slats, the distance between slats, the sizeof the tetrahedrons and octahedrons, and the degree of truncation, thedimensions of the core can be adapted to the unique rigidity, height,weight and other engineering needs of each manufactured application.

Truncation provides other benefits as well: It can reduce the pressuresrequired to mold the core; and it can provide additional surface areafor bonding when the core is used in laminates.

By virtue of being one piece, the lattice also can serve as a deliveryvehicle for liquids, gases, and other molecular and atomic particles ifthe lattice is defined by a vacuum or gas or permeable substanceconstrained by the aforementioned tessellation of truncated ornon-truncated tetrahedra and octahedral elements. While in themanufacturing of a core, material would in most instances be removedfrom the negative space, in applications such as a delivery vehicle,material can be introduced into the negative space, leaving the corearea available to disperse the substance being delivered. In essence,one would “mold” the mold, and assemble the two halves leaving thelattice as the empty space.

In other applications the core can be formed and then the negative spacecan be filled with a different material with complementary properties.For example, the core can be made of a rigid, solid material and foamcan be injected into the negative space to provide insulation to arefrigerated space. Alternatively, the foam can be molded to resemblethe two halves of the mold and then the two halves can be assembledaround the lattice.

In some embodiments, the tetrahedral and/or octahedral shapes(non-truncated or truncated) may be irregular in order to provide forefficient molding and/or mold release. In some embodiments, thetetrahedral and/or octahedral shapes (non-truncated or truncated) may beirregular in order to provide for desired lattice wall thicknesses,and/or to enhance or compensate for properties of the material ormaterials used to form the lattice, and/or to introduce a curvature.

Methods

Another embodiment described herein is an elegant and low cost method ofproducing a Tetrahedral-Octahedral Honeycomb lattice. The method employsan appropriately designed injection mold or compression mold (casting).The core, sheet, or other structure can be manufactured in any moldablematerial (plastic, aluminum, steel, or concrete, for example) whichwould make a desirable lattice core structure.

One embodiment is a method of producing a core, sheet or other materialthat involves truncating the top and bottom of the structure to open upthe peaks of the tetrahedral and octahedral elements. This provides moresurface area for bonding laminated sheets of material and reduces thepressure required to mold the lattice. It also reduces the weight of thelattice and provides a means of adjusting the height. The manufacturingprocess of the modified lattice is, in many respects, the same as theoriginal core-lattice structure.

The product described herein can be used in place of conventionalhoneycomb material. While a hexagonal honeycomb laminate handlescompressive forces well, the geometry of hexagonal honeycomb does nothandle shear and a variety of other forces well. To compensate, avariety of materials have been employed to produce the hexagonalhoneycomb structure (for example aluminum and Kevlar) to compensate forthese shortcomings. Also, a variety of sheet materials have beenlaminated to honeycomb cores to improve the composite structures'performance under the anticipated conditions of use. The result has beenan increase in manufacturing complexity and cost.

Furthermore, low-margin, cost sensitive applications that could benefitfrom the high strength to weight ratio of a honeycomb-type core materialhave been precluded from using conventional honeycomb technology due tocost considerations. A principal objective of the method describedherein is to manufacture a core material which possesses inherentquasi-isotropic or isotropic properties, and/or enhanced performanceproperties including tension, compression, shear, bending and torsionalrigidity. But unlike prior known manufacturing techniques, theembodiments described herein seek to produce this core materialdirectly, in one piece, and at a substantially reduced cost.

The mold to produce the lattice fills the voids in the lattice whileleaving space for the resin or other structural material to flow andharden into lattice. Filling the Regular Convex Tetrahedral voids isstraightforward. The top and bottom mold components simply need to haveoffsetting parallel rows of RCT with the triangular base of the RCTbuilt into the mold base and top, and one side of all of the RCT in therow aligned along a common plane. It is noted that the planes ofalignment of the sides of the RCT are at an angle to the base or top ofthe lattice equal to the dihedral angle of an RCT (70.53 degrees).

The method of filling the octahedral voids which alternate with the RCTin the tetrahedral rows of the lattice is non-trivial but elegant. Notethat the RCO alternating with the RCT have a face which is also alignedalong the common plane of the tetrahedral faces in the same row. Thedisclosed embodiments are based on the fact that an RCO is composed oftwo Pyramids (see definition above) with Pyramids' adjacent square basesaligned on a diagonal plane. As noted in the definitions above, thetriangular sides of the Pyramids are congruent to the faces of the RCT.As a result, when the 2 sides of the mold are released at an angle equalto the diagonal orientation of the square bases of the Pyramids, thevoid-filling Pyramids can be removed from the top and bottom of the RCOleaving the lattice.

In another method, the tetrahedral-octahedral honeycomb lattice isprinted using an additive manufacturing process. When this technique isused, in embodiments, post-treatment and or fiber-reinforcementtechniques are employed to ensure that the resulting product exhibitsquasi-isotropic or isotropic qualities.

Referring to the drawings, FIG. 1 shows a perspective view of a sheet 10according to a first embodiment. The sheet is three dimensional. FIGS.2A-2G show other views of the sheet of FIG. 1. The sheet hassubstantially isotropic properties due to its geometry. FIG. 3 shows atop plan view of the sheet. The bottom plan view looks generally thesame as the top plan view.

FIGS. 4-6 illustrate a second embodiment of a sheet 110 in which thetetrahedral and octahedral portions are truncated along the oppositefirst and second faces. It is noted that in other embodiments, one facehas truncated tetrahedrons and/or octahedrons while the other face doesnot. Furthermore, in embodiments, there may be truncation of only someof the tetrahedral portions and/or octahedral portions within a singlesheet. In certain embodiments, some of the tetrahedral portions aretruncated while other tetrahedral portions are not truncated. In certaincases, some of the octahedral portions are truncated while otheroctahedral portions are not truncated. In some embodiments, some or allof the tetrahedral portions are truncated while the octahedral portionsare not truncated. In certain embodiments, some or all of the octahedralportions are truncated while the tetrahedral portions are not truncated.

FIGS. 7A-7E show perspective views of a first mold section 220 and asecond mold section 221 that can be used to mold the sheet shown inFIGS. 1-3. The first mold section 220 has a series of alignedtetrahedrons 222. In between the tetrahedrons 222, a series of alignedregular square pyramids 224 are positioned. Each pyramid 224 ispositioned sideways, with the base 226 of the square pyramid extendingat an angle relative to a horizontal plane. In FIG. 7A, the top moldhalf 221 is disposed vertically to show the inner side. The top moldhalf 221 include a plurality of aligned regular square pyramids 234,each with a base 236. The tetrahedrons 232 on the top mold half 221 canbe seen in FIG. 7B. FIG. 7B shows the mold of FIG. 7A in a closedposition. The space between the protrusions on the top mold half andbottom mold half are filled with moldable material in order to form thelattice. FIG. 7C shows the mold in a closed position with slats showingthe spaces where sheet material fills the mold. The square bases of thepyramids on the top mold half are in contact with the square bases ofthe pyramids on the bottom mold half, and the combination of the upperand lower pyramid pairs forms the octahedral spaces in the lattices.

FIG. 7D shows the mold of FIG. 7A in a partially open position. As canbe seen, the direction of pull is parallel to the plane of the pyramidbases. FIG. 7E shows the mold of FIG. 7A in an open position.

FIG. 8 shows a schematic view of a closed mold during molding. The firstmold section 320 has alternating tetrahedrons 322 and inclined pyramids324 (pyramids that are positioned sideways, with one triangular faceparallel to the length of the first mold section 320, and the squarebase 326 of the pyramid extending diagonally upward relative to thelength of the first mold section 320), as can be seen in FIGS. 7A-7D.The second mold section 321 also includes a plurality of alternatingtetrahedrons 332 and inclined pyramids 334. The second mold section 321is configured to be complementary in order that, substantiallythroughout the mold, a base 326 of the inclined pyramid 324 is insubstantially complete contact with a base 336 of the inclined pyramid334 with no space therebetween, such that an octahedral void is createdduring molding. Thus, the material used to form the sheet 310 isprevented from moving between the two rectangular bases of each pyramid324 and its complementary pyramid 334 during molding.

Movement of the mold parts and the molded sheet can be seen in FIGS.9-12. To remove a molded sheet 310, one or both mold sections are moved,and the direction of movement is at an angle relative to the plane ofthe sheet 310. As is shown in FIGS. 9, 11 and 12, the mold sections areremoved in directions that are parallel to the bases of the base-to-basepyramids that define the octahedral portion of the mold when the mold isin a closed position. For a right regular pyramid, the dihedral anglebetween the plane of the square base and the plane of a triangular sideis 54.735 degrees. This is half of the dihedral angle of a regularconvex octahedron, which as indicated above, is 109.47 degrees. (Statedin general terms, because one triangular side of the regular squarepyramid is coplanar with the mold base, the square base that is definedby each of the two pyramidal shapes that form one octahedron is angledrelative to the plane of the mold base.) The upward and sidewarddirection that the second mold section 321 is moved when the mold isopened is about 35.3 degrees away from a vertical direction, and about54.7 degrees away from a horizontal direction. Similarly, if the firstmold section 320 is moved in a downward and sideward direction, as inthe embodiment shown in FIG. 11, the first mold section 320 is moved ina direction that is about 35.3 degrees away from a vertical directionand about 54.7 degrees away from a horizontal direction. In theconfiguration shown in FIG. 12A, the second mold section 321 moves in a“left” sideward direction and the first mold section 320 moves in a“right” sideward direction. As is sometimes the case in moldingoperations, the line of draw can be slightly different from a directline of draw in order to facilitate removal of the molded piece.

For cases in which both mold sections are moved away from the sheet, thesecond mold section 321 can be removed first (FIG. 9), the first moldsection 320 can be removed first (FIG. 11), or both mold sections can beremoved at the same time (FIG. 12A, and also FIG. 12B, which shows firstmold section 370 and second mold section 371). For cases in which onemold section is removed and the mold includes a sheet ejector (see, forexample, FIG. 10, which includes retractable ejector pins 344), thesheet is ejected in generally the same angular direction as the movementof the mold section that is first removed. As is shown in FIG. 10, ifthe second (upper) mold section 321 is removed first, in the directionshown in FIG. 9, the sheet 310 can be ejected from the first (lower)mold section 320 in a direction generally parallel to the direction ofmovement of the second mold section 321.

In embodiments, the second mold section can be moved, before, after, orat the same time as the movement of the first mold section. Furthermore,in some cases, (see FIG. 11), if the first mold section 320 is movedaway from the sheet, the sheet 310 will drop from the second moldsection 321 due to gravity. In other embodiments, after the first(lower) mold section 320 is moved away from the sheet 310, the sheet isejected from the second (upper) mold section 321 in a direction parallelto the angular movement of the first mold section 320 using a suitableejection technique.

FIGS. 12A and 12B show simultaneous movement of the upper and lower moldsections away from the molded sheet. FIG. 12A shows an embodiment inwhich the sheet is positioned horizontally during molding. FIG. 12Bshows an embodiment in which the sheet is positioned at an angle duringmolding, with the direction of pull of the upper mold half beingvertically up and the direction of pull of the lower mold half beingvertically down.

FIGS. 13-17 show a mold that is generally similar that that of FIGS.7-12 except that the tetrahedral and/or octahedral portions of the moldare truncated, and the mold has vertical pulls such that the sheet isangled during molding. Movement of the first mold section 420, thesecond mold section 421 and the sheets 410 are similar to the movementsdescribed above in connection with FIGS. 7-11, except that the planes ofmolded sheets are positioned at an angle relative to a horizontal plane.More specifically, FIG. 13 shows closed mold sections 420 and 421. FIG.14 shows the upward movement of second mold section 421. FIG. 15 showsupward movement of the sheet off of first mold section 420. FIG. 16shows downward movement of first mold section 520. FIG. 17 showsdownward movement of first mold section 620 and upward movement ofsecond mold section 621.

FIG. 18 depicts a top view of an embodiment of sheet material 210 havingclosed sides around the perimeter of the four-sided lattice.

In embodiments, the lattice is post-treated to impart desiredcharacteristics. Non-limiting examples of post-treatment techniquesinclude coating, impregnating, compressing, curing, post-curing,heating, cooling, wetting, abrading, solvent treatment, washing,rinsing, grinding, irradiating, sintering, bending and/or sterilizing.

A Method of Making a Mold

In the description of the technique for molding a single piecetetrahedral-octahedral honeycomb core structure, the focus was on theindividual elements of the negative space comprising the mold (thetetrahedra and pyramid-pairs forming the octahedra). In embodiments, theactual machining of the mold is much more elegant. In one embodiment,given a block of aluminum, steel or other material from which themold-halves are to be machined, the removal of material is along 4 setsof parallel planes, 3 of which are defined by the non-horizontal sidesof the tetrahedra (relative to the sheet plane), and one which isdefined by the base plane of the pyramids which form ½ of the octahedra(see FIG. 7F). The base plane of the pyramids and one of the planes ofthe tetrahedra run along a common axis, albeit at different angles whichintersect at the base of a given mold-half. As can be seen in FIG. 7F,the space between these two planes forms a wedge which eventually ismachined out in its entirety to make room for the top half of the mold.The width of the material removed along the parallel planes defined bythe tetrahedra corresponds to the desired width of the latticecomprising the honeycomb.

These machined cuts form ½ of the mold. If this is the bottom half ofthe mold, then the top half is a mirror image of the bottom half and ismachined the same way. Details on mold material insertion/injection andend-product extraction will vary depending upon the materials andmethods of the application. Details on the construction of the sides ofthe mold also will vary depending upon the materials and methods of theapplication being manufactured. In embodiments, machining is performedwith a router.

In other embodiments, the top and bottom halves of the mold can be madeusing additive manufacturing.

Additive Manufacturing

Recent advances in software technology have enabled the manufacture of avariety of product designs through the use of additive manufacturing.ISO/ASTM52900-15 defines seven categories of additive manufacturingprocesses as being examples of 3D printing, namely Binder Jetting,Directed Energy Deposition, Material Extrusion, Material Jetting, PowderBed Fusion, Sheet Lamination and Vat Photopolymerization. The sheetmaterial and core material described above can be made using additivemanufacturing. In embodiments, the additive manufacturing technique thatis used produces the material as a one-piece component. That is, nolamination, soldering or welding is required of two or more separateparts. In some cases, the production driver used in additivemanufacturing is organized around the tetrahedral and octahedralelements, in order that the additive manufacturing device can “print”the sheet material around separate octahedral and tetrahedral elements.

If vat polymerization is used, the liquid or molten polymer isirradiated, often using UV light, to convert that liquid or moltenmaterial into a solid. If stereolithography is used, astereolithographic machine converts the liquid or molten plastic into asolid.

Polymeric materials used in 3D printing include a variety ofthermoplastic and thermoset materials, and composites incorporatingfillers, including carbon or metallic materials.

In some cases, the sheet material is fabricated using a 3D printer thatuses fused filaments. In embodiments, the 3D printed sheet material ispost-treated to further improve its tensile strength, such as by coatingthe sheet material with a coating applied by spraying, dipping or thelike. In embodiments, the material used in additive manufacturing is afiber-reinforced polymer, thereby imparting additional strength,including favorable tensile strength and stiffness, to the finalproduct.

Non-limiting examples of polymers that can be used in 3D printinginclude acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA).These polymers can be fiber reinforced, with carbon fibers or anothersuitable type of fiber.

One embodiment disclosed herein is a lightweight, strong sheet materialformed by additive manufacturing. In embodiments, the sheet material iscarbon-reinforced material in order to impart favorable stiffness andtensile strength to the sheet material while making it lightweight. Insome cases, the build direction of the material, i.e., the direction inwhich the nozzle moves when forming each layer, is parallel to thedirection in which the greatest tensile strength is desired, therebyreducing the likelihood of breakage.

3D printed thermoset polymers can be cured during manufacture byphotopolymerization, such as with UV light, or can be post-cured, suchas by heating.

In embodiments, the 3D printed sheet material is post-processed using asuitable solvent, such as acetone or methyl ethyl ketone. The solventcan be used to smooth the sheet material or hold pieces together. Invacuum treatment, heat is applied to evaporate the solvent so that itinteracts with the surfaces of the sheet material in a closed container.

In embodiments, internal tetrahedral and octahedral supports are usedduring printing to support “overhanging” features of the sheet material,such as diagonal walls. These supports may have the configuration of themold halves shown in the photographs included herein.

Other types of post-treatment include application of a strengtheningthin layer of a polymeric coating composition, as well as the types ofpost-treatments described above.

EXAMPLES Example 1

Simulations were conducted to determine physical properties oftetrahedral-octahedral honeycomb lattice formed from polycarbonate withan aluminum skin on the top and bottom surfaces. The samples had alength of 3 inches, a width of 8 inches, and a total thickness of0.468-0.500 inches including the skin. Some of the samples had truncatedtetrahedral-octahedral honeycomb lattice. The sample dimensions and thefinite element analysis test results for Beam Load and Shear Loadsimulations are shown on FIGS. 19 and 20 below. “Cell thk (in)”indicates cell wall thickness in inches.

Beam loading test were conducted as per MIL-C-7438. Shear loading testswere conducted as per ASTM C-273. Cell size was measured along one sideof the triangles from the wall centers, as viewed from the top of thelattice.

Prophetic Example 2

Tetrahedral-octahedral honeycomb core samples measuring 1 foot by 1 footby ½ inch with a wall thickness of about 0.045 inch are made fromaluminum. The lattice optionally can be sandwiched between two aluminumskin sheets.

Prophetic Example 3

Tetrahedral-octahedral honeycomb core samples measuring 1 foot by 1 footby ½ inch with a wall thickness of about 0.045 inch are made fromstainless steel. The lattice optionally can be sandwiched between twoaluminum skin sheets.

Prophetic Example 4

Tetrahedral-octahedral honeycomb core samples measuring 9 inches by 9inches by ¾ inch with a wall thickness of about 0.045 inch are made fromaramid fiber. The lattice optionally can be sandwiched between twoaluminum skin sheets.

Prophetic Example 5

Tetrahedral-octahedral honeycomb core samples measuring 2 foot by 1 footby ½ inch with a wall thickness of about 0.045 inch are made from Kevlaror Nomex aramid fiber. The lattice optionally can be sandwiched betweentwo aluminum skin sheets.

Prophetic Example 6

Tetrahedral-octahedral honeycomb core samples measuring 2 foot by 1 footby ½ inch with a wall thickness of about 0.045 inch are made frompolypropylene. The lattice optionally can be sandwiched between twoaluminum or stainless steel skin sheets.

Applications of the Tetrahedral—Octahedral Honeycomb Lattice

The lattice can be useful anywhere a lightweight, quasi-isotropicstructural core material/laminate would be beneficial, including, butnot limited to, the following:

-   -   1) Aerospace: Airplane Flooring, Bulkheads, Engine Turbine        Blades, Hull    -   2) Trucking: Trailer siding, Refrigerated Trailer siding,        Flooring, Doors    -   3) Building and Construction: Doors, Garage Doors, Walls,        Concrete Cinderblocks    -   4) Shipping: Pallets, Corrugated Cardboard, Shipping Containers    -   5) Marine: Bulkheads, Doors, Flooring, Hull    -   6) Solar Panels—Backing Material Supporting Solar Receiver    -   7) Decorative—Lightweight, Rigid, Decorative Panel    -   8) Wind Energy—Wind Turbines    -   9) FEMA Trailers—Sides of lightweight FEMA Housing    -   10) Recreational Vehicles—Sides of Superlight RVs    -   11) Ballistic Protection—Ballistic Protection Panels for        Military Vehicles    -   12) Unmanned Undersea Vehicles—Bulkheads, Hull, Flooring, Doors,    -   13) Rail—Floor, Bulkhead, Doors, Decorative Panels    -   14) Automotive—Ballistic Protection, Crash Panels, Floor Panels    -   15) Highway—Crash Barrels, Sign Backing    -   16) Advertising—Billboards    -   17) Other—Flat Panel TV, Lightweight Drywall Alternative,        Alternative to Plywood, Stealth Benefits, Acoustic Dampening,        Support for insulation integrated into voids    -   18) Dissipation of material like drugs through the lattice if        the lattice area is left void and the mold structure is left in        place to form the lattice-void. In this application, one would        “mold” the two halves of the mold and then assemble the two        halves to form the final product.

A number of alternatives, modifications, variations, or improvementstherein may be subsequently made by those skilled in the art, which arealso intended to be encompassed by the following claims.

What is claimed is:
 1. A one-piece component comprising atetrahedral-octahedral honeycomb lattice.
 2. The one-piece component ofclaim 1, wherein the component is isotropic.
 3. The one-piece componentof claim 1, wherein the component is quasi-isotropic.
 4. The one-piececomponent of claim 1, wherein the component comprises substantiallyflat, parallel first and second faces.
 5. The one-piece component ofclaim 1, wherein the component comprises curved, generally parallelfirst and second faces.
 6. A structure comprising the one-piececomponent of claim
 1. 7. The structure of claim 6, comprising at leastone of a floor, a ceiling, a wall, a door and a compartment of at leastone of a building, a vehicle, an aircraft, a watercraft, a train, or acover of at least one of a floor, a ceiling, a wall, a door and acompartment of at least one of a building, a vehicle, an aircraft, awatercraft, a train.
 8. The structure of claim 6, comprising at leastone of a turbine blade, a pallet, a shipping container and a roadsidefixture.
 9. A one-piece component comprising a truncatedtetrahedral-octahedral honeycomb lattice.
 10. The one-piece component ofclaim 9, wherein the component is isotropic.
 11. The one-piece componentof claim 9, wherein the component is quasi-isotropic.
 12. The one-piececomponent of claim 9, wherein the component comprises substantiallyflat, parallel first and second faces.
 13. The one-piece component ofclaim 9, wherein the component comprises curved, generally parallelfirst and second faces.
 14. The one-piece component of claim 9, whereinat least some of the tetrahedral portions of the tetrahedral-octahedralhoneycomb lattice are truncated.
 15. The one-piece component of claim 9,wherein at least some of the octahedral portions of thetetrahedral-octahedral honeycomb lattice are truncated.
 16. Theone-piece component of claim 9, wherein at least some of the tetrahedralportions and at least some of the octahedral portions of thetetrahedral-octahedral honeycomb lattice are truncated.
 17. Theone-piece component of claim 9, wherein substantially all of thetetrahedral portions and octahedral portions of thetetrahedral-octahedral honeycomb lattice are truncated.
 18. A structurecomprising the one-piece component of claim
 9. 19. The structure ofclaim 18, comprising at least one of a floor, a ceiling, a wall, a doorand a compartment of at least one of a building, a vehicle, andaircraft, a watercraft and a train, or a cover for a portion of at leastone of a floor, a ceiling, a wall, a door and a compartment of at leastone of a building, a vehicle, and aircraft, a watercraft and a train.20. The structure of claim 18, comprising at least one of a turbineblade, a pallet, a shipping container and a roadside fixture.